DEPARTMENT OF THE INTERIOR 

Franklin K. Lane, Secretary 


United States Geological Survey 

George Otis Smith, Director 


Bulletin 620—N 


THE AZTEC GOLD MINE 

BALDY, NEW MEXICO 


BY 


WILLIS T. LEE 


Contributions to economic geology, 1915, Part I 
(Pages 325-330) 

Published January 15,1916 



WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1916 


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DEPARTMENT OF THE INTERIOR 

Franklin K. Lane, Secretary 


United States Geological Survey 

George Otis Smith, Director 

Bulletin 620 —N 


THE AZTEC GOLD MINE 

BALDY, NEW MEXICO 


BY 

WILLIS T. LEE 

\ 


Contributions to economic geology, 1915, Part I 
(Pages 325-330) 

Published January 15, 1916 



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WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1910 







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CONTENTS. 

Page. 

Introduction. 325 

Discovery and development. 325 

Geography. 327 

Geology. 327 

Occurrence of ore. 329 


ILLUSTRATIONS. 

Page. 

Figure 19. Map showing Baldy Peak and Aztec mine, Baldy, N. Mex. 328 

20. Sketch profile through Baldy Peak and Aztec mine, Baldy, N. Mex.. 329 

21. Sketch profile illustrating the occurrence of gold ore on the down- 

slope side of anticlinal ridges at Baldy, N. Mex. 330 

ii 

D. of D. 

FEB 23 1916 












THE AZTEC GOLD MINE, BALDY, NEW MEXICO. 


By Willis T. Lee. 


INTRODUCTION. 

Interest has recently been revived in the Aztec mine at Baldy f 
Colfax County, N. Mex., which was first described bv Raymond 1 
m 1870 and later by Jones 2 and Graton, 3 by the discovery of a large 
body of high-grade gold ore. This mine, situated on the Maxwell 
land grant, was a famous producer 45 years ago, but after the exhaus¬ 
tion of the body of ore then worked the mine attracted little atten¬ 
tion. An adit, started a few years ago, was driven through several 
small deposits of moderately rich ore and in August, 1914 , entered 
a large body of high-grade ore. This ore body has yielded good 
returns. Its extent had not been ascertained at the time of the 
writer’s investigation in July, 1915. 

DISCOVERY AND DEVELOPMENT. 

The Aztec mine, owned and operated by the Maxwell Land Grant 
Co., is situated at an altitude of more than 10,000 feet above sea 
level, on the eastern slope of Bakly Peak, which reaches an altitude 
of nearly 12,500 feet. The mine is connected by wagon road with 
Ute Park, the present terminus of the St. Louis, Rocky Mountain 
& Pacific Railway, a branch line of the Santa Fe System. Accord¬ 
ing to a published report the gold was discovered on Baldy Peak 
by a man prospecting for copper, which had previously been found 
there. The account states that an Indian who came to Fort Union 
on a trading expedition exhibited some specimens which he had 
picked up on the peak. The white men at the fort recognized them 
as copper ore and sent one of their number with the Indian, who 
showed him where the ore was found. This resulted in the location 
of a prospect which for several years was known locally as the Copper 
mine, but which later became known as the Mystic lode. It is on 
the west side of Baldy Peak, near the top, at an altitude of about 
12,200 feet. 

1 Raymond, R. W., Statistics of mines and mining in tlie States and Territories west of the Rocky Moun¬ 
tains for 1S69, pp. 3S5-3S8, 1870. 

2 Jones, F. A., Mines and minerals of New Mexico, pp. 144-151,1904. 

2 Lindgren, Waldemar, Graton, L. C., and Gordon, C. H., The ore deposits of New Mexico: U. S. Geol. 
Survey Prof. Paper 68, pp. 92-105,1910. 

16340°—16 


325 





326 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1915, PART I. 

A considerable amount of development work was done at various 
times on this prospect, but its great altitude and its distance from 
a railroad shipping point prevented profitable operation. However, 
when a railroad was constructed to Ute Park in 1906 it was thought 
that some of the best ore might be shipped with profit. One car¬ 
load, yielding 20 per cent of copper, was later sent to the smelter. 
At the time of the writer’s visit another carload was ready for ship¬ 
ment. The ore is carried by burros down the mountain to Baldy 
and thence carted by wagon to Ute Park, a distance of 8 miles. 
The present opening is not sufficiently developed to permit a determi¬ 
nation of the size of the ore body or its relation to the rocks con¬ 
taining it, but from what may be seen it is probable that the ore 
occurs in a fissure vein. It consists of chrysocolla and cuprite, 
the former predominating. The cuprite occurs as dark-red, clearly 
defined angular fragments embedded in the bluish-green chrysocolla, 
the mass resembling a cemented breccia. 

According to the published account a party sent out in 1866 to do 
development work on the copper prospect found placer gold on 
Willow Creek, on the west slope of Baldy Peak, in October of that 
year. The news of this discovery spread rapidly, and in the summer 
of 1867 placer mining was begun in this region, which later became 
known as the Elizabethtown district. These placers were worked 
for several years, and according to Jones 1 about $2,250,000 worth of 
gold was recovered. However, the scarcity of water made operation 
expensive, and although only a small part of the placer ground has 
been worked, no extensive operations have been carried on there for 
several years. The placer gold was found only along streams heading 
on Baldy Peak, and this led to a search of its slopes for the lode. In 
June, 1868, the outcrop was discovered, and later the Aztec mine was 
opened on it. The mine was rapidly developed, and a 15-stamp mill 
was put into operation October 29, 1868. For a few years the yield 
was sometimes as high as $21,000 a week. Raymond 2 reported in 
1870 that ore from this mine averaged as high as $68.83 a ton saved 
on the plates. It is estimated, according to Graton, 3 that the total 
amount of gold taken from this mine was “ between $1,250,000 and 
$1,500,000, of which about $1,000,000 was taken out in the first four 
years.” 

This mine brought the district into prominence and is said to have 
been the immediate cause of the sale to an English syndicate of the 
Maxwell land grant, consisting of 1,750,000 acres. The original 
grant was made by Mexico in 1843, but its boundaries, as claimed, 
were called into question by the officials of the United States Gov¬ 
ernment until 1861, when Congress confirmed the grant. The body 


1 Jones F. A., op. cit., p. 145. 2 Raymond, R. W., op. cit., p. 3S7. * Graton, L. C., op. cit., p. 97. 




327 




THE AZTEC GOLD MINE, BALDY, N. MEX. 

m 

of the ore which had yielded the rich returns was soon exhausted. 
In 1872 the mine became involved in litigation and mining operations 
ceased. Thereafter for more than 40 years occasional efforts w~ere 
made to find other bodies of paying ore. Accounts of these attempts 
are contained in the reports cited. The sedimentary rocks of the 
district are faulted and intruded by igneous rock in the form of dikes 
and sills. Near these bodies of igneous rock and in the zone of frac¬ 
ture many prospects have been opened, and in some of them small 
quantities of ore have been found, but none that yielded notable 
returns. 

In 1909 J. T. Sparks, then in charge of the development work at 
Baldy, ascertained that a quartzose conglomerate, now known to 
constitute the base of the Raton formation in this region, is the 
“quartzite” and that the underlying Pierre shale, of Cretaceous age, 
is the “slate” of the old Aztec workings. He confined his attention 
to this contact and found ore in several places. In the extension 
of one of the entries started on this contact his successor, E. V. 
Deshayes, found the body of ricli ore which is being worked at the 
present time. 

GEOGRAPHY. 

Baldy Peak (fig. 19) is the highest point of a prominent ridge which 
Graton called the Cimarron Range and which is separated from the 
main range of the Rocky Mountains by Moreno Valley, a troughlike 
basin draining eastward by a narrow canyon cut through this range 
by Cimarron River. Because of its great altitude Baldy Peak receives 
relatively heavy precipitation, but the mine is situated on the steep 
slope so near the head of Ute Creek that the streams are small and 
difficulty is experienced in obtaining enough water for mining opera¬ 
tions. Farther down Ute Creek there is a small, steady flow that has 
been utilized for many years in placer mining. 

GEOLOGY. 

Only two sedimentary formations crop out in the vicinity of 
Baldy—the Pierre shale, of Cretaceous age, and the Raton formation, 
of early Tertiary age. At Ute Park and localities farther east the 
Pierre shale is overlain by the Trinidad sandstone and the Vermejo 
formation, both of Cretaceous age. The Vermejo contains the most 
valuable coal beds of the Raton coal field. These formations are 
overlain unconformably by the Raton formation, and between Ute 
Park and Baldy the Trinidad and Vermejo were eroded away before 
the sediments of the Raton were deposited, so that the Raton now 
lies across beveled edges of the older rocks, as indicated in figure 20. 

The sedimentary formations, which were originally almost hori¬ 
zontal, are now faidted and upturned on the flanks of the mountain. 
Minor folds and small faults, formed probably at the time the beds 


328 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1915, PART I. 



V 





































THE AZTEC GOLD MINE, BALDY, N. MEX. 


329 


were upturned, antedate the deposition of the ore. The movements 
that produced these faults and folds occurred some time after the 
beginning of the Tertiary period, for the beds of early Tertiary age— 
the Raton formation—are involved in them. 

The igneous rock of the district consists of quartz monzonite por¬ 
phyry an d occurs as dikes and sills. The sills are numerous, and 
y them were intruded into the Pierre shale, although some 
occur also in the Raton lormation; the dikes cut both formations. 
Inasmuch as these igneous rocks cut the Raton formation, the 
intrusion was of post-Raton date and possibly accompanied the 
uplifting of the sedimentary beds. A prospect tunnel driven into 
the west side of the mountain in penetrating a thickness of 1,400 
feet of rock went through six sills aggregating 425 feet in thickness. 
As Graton has pointed out, these intrusive rocks have effected pro¬ 
nounced local metamorphism of the shales. 



Figure 20.—Sketch profile through Baldy Peak and Aztec mine, Baldy, N. Mex., showing the uncon¬ 
formity between the Raton formation and the Pierre shale. The gold ore at Baldy occurs along this 
unconformity. 

OCCURRENCE OF ORE. 

The gold ore is clearly associated with the igneous rock, and many 
of the small ore deposits of the district are reported to occur at the 
contact of this rock with the shale. However, the principal bodies 
of ore known at the present time are not in immediate contact with 
the intrusive rock. 

The principal bodies of ore near Baldy occur at the plane of the 
post-Cretaceous unconformity, where the basal conglomerate of the 
Raton formation rests on the Pierre shale. The ore was deposited 
during the Tertiary period, at some time later than the Raton epoch. 
Some of the ore is found in small pockets and stringers in the con¬ 
glomeratic sandstone, but most of it that is worked at the present 
time is in the underlying shale, into which it extends for distances 
of a few inches to 5 feet or more. The richest and largest bodies 
occur on the down-slope side of the crests of the minor folds, as 
illustrated in figure 21. 

The folding seems to have fractured the shale at the crests and 
opened minute fissures. Many of these openings are now filled with 
calcite, which appears as an intricate network in the shale. The cal- 
cite carries pyrite, chalcopyrite, sphalerite, and possibly galena. 
Pyrite also occurs very generally along the contact. The gold occurs 















330 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1915, PART I. 

in part as wire gold or as thin irregularly shaped masses, as if depos¬ 
ited in cavities, hut usually in minute particles coated with dark 
material, so that to the eye they do not appear metallic. In some 
places these particles appear to be rather generally distributed 
through the shale, but in others they occur especially in dark nodu¬ 
lar masses of heavy fine-grained crystalline rock that apparently 
consist chiefly of chlorite. These masses are particularly sought for 
in mining, for they constitute the richest ore. Their origin was not 
ascertained. 

The ore is free milling and is treated in a 10-stamp mill, by far the 
greater part of the gold being caught on the amalgamating plates. 
The concentrates are sent to the smelter and the tailings are im¬ 
pounded for future treatment. 

Until recently the greater part of the ore mined came from the 
lower part of the conglomeratic sandstone or from the fractured 

portions of the shale 
close to the contact. 
Sparksfound it mostly 
in a rusty zone be¬ 
tween the sandstone 
and the shale in cal¬ 
careous gangue mat¬ 
ter, mainly as free gold 
but also in the sul¬ 
phides. He reported “ sulphides and arsenides of silver, copper, 
nickel, and cobalt” in association with the gold and stated that the 
sulphides occurred most abundantly near the contact, while the free 
gold was more often found along slips and fractures ranging from a few 
inches to a few feet in width both above and below the main cbntact. 
The gold-bearing solutions seem to have penetrated everything near 
the contact, but the rich ore body now being worked indicates that 
they deposited gold most readily in the shale. As elsewhere in this 
region, the conglomeratic sandstone contains small irregular masses of 
coal, probably derived from buried wood. A piece of such coal from 
one of the openings of the Aztec mine was assayed by E. E. Bur¬ 
lingame & Co., of Denver, who report that the ash from the coal 
runs 8 cents a ton in gold. 

The ore handled at the time of the writer’s visit was reported to 
range in value from $15 to $250 a ton. During the 10 months prior 
to the visit more than 2,100 tons had been treated, with an average 
return of $107.60 a ton. Of this yield 80 per cent was recovered by 
amalgamation and 20 per cent was derived from- the concentrates. 
A small amount of gold, which will probably be recovered in time, 
still remains in the tailings. 



Figure 21. —Sketch profile illustrating the occurrence of gold ore 
on the down-slope side of anticlinal ridges at Baldy, N. Hex. 


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